1. Field of the Invention
The present invention relates to an aluminum nitride sintered body and a method of producing the same, and to a metal including member used as a function gradient member in which a metal member is embedded in an aluminum nitride sintered body. Moreover, the present invention especially relates to an electrostatic chuck preferably used in a semiconductor manufacturing apparatus.
2. Related Art Statement
Generally, an electrostatic chuck is used for chucking a semiconductor wafer in film forming steps of transferring, exposing, chemical vapor depositing, and spattering the semiconductor wafer, or in steps of micro-machining, washing, etching, and dicing. As a substrate member of the electrostatic member, a densified ceramics is sometimes used. Particularly, in a field of semiconductor manufacturing apparatuses, a halogen corrosive gas such as CIF is frequently used as an etching gas or a cleaning gas. Moreover, in order to rapidly heat or cool the semiconductor wafer while the semiconductor wafer is chucked, it is desirable that the substrate member of the electrostatic chuck has a high thermal conductivity. Further, in order not to fracture the substrate member due to a rapid temperature variation, it is desirable that the substrate member has a thermal shock resistivity. A densified aluminum nitride has a high corrosion resistivity with respect to the halogen corrosive gas mentioned above. Moreover, it is known that aluminum nitride has a high thermal conductivity and its volume resistivity is greater than 10.sup.14 .OMEGA..multidot.cm. Further, it is known that aluminum nitride has a high thermal shock resistivity. Therefore, it is preferred to form the substrate member of the electrostatic chuck for the semiconductor manufacturing apparatus using an aluminum nitride sintered body.
On the other hand, in the semiconductor manufacturing apparatus, in order to use the electrostatic chuck as a suscepter for holding the semiconductor wafer, it is necessary to decrease the resistivity of the substrate member. For example, in Japanese Patent Publication No. 7-19831, in order to improve a chucking property of the electrostatic chuck, the volume resistivity of an insulation dielectric layer of the electrostatic chuck is decreased to smaller than 10.sup.13 .OMEGA..multidot.cm by mixing a conductive material or a semiconductive material into an insulation member having a high volume resistivity. Moreover, in Japanese Patent Laid-Open Publication No. 2-22166, ceramic raw materials made of alumina as a main ingredient are sintered under a reduction atmosphere to produce a dielectric ceramic for the electrostatic chuck. In this case, 1-6 wt % of alkali earth metal and 0.5-6 wt % of transition metal, both shown as a weight of oxide, are included in the ceramic raw materials. In this method, for example, a dielectric rate is improved by mixing TiO.sub.2 into alumina ceramics and a volume resistivity is decreased to 10.sup.12 -10.sup.18 .OMEGA..multidot.cm, to obtain a high chucking property.
However, the volume resistivity of a highly purified alumina nitride sintered body is greater than 10.sup.14 .OMEGA..multidot.cm, and thus it is too high to use as the substrate member of the electrostatic chuck for the semiconductor manufacturing apparatus. In this case, in order to obtain a sufficient chucking property, it is necessary to form an extremely thin insulation dielectric layer having a thickness smaller than 300 .mu.m. However, if the insulation dielectric layer is thin as mentioned above, there is a possibility of generating an insulation fracture and so on from one of the reaction layers in a surface of the insulation dielectric layer. From this point of view, we understand that it is preferred to make the thickness of the insulation dielectric layer greater than 500 .mu.m.
However, in the known electrostatic chuck made of aluminum nitride, if the insulation dielectric layer is made thick as mentioned above, a chucking property of the electrostatic chuck is decreased, and thus it is difficult to obtain a sufficient chucking property particularly in a low temperature region in which a volume resistivity is high. Usually, a dry etching process is performed under a low temperature of -50.degree. C..about.-60.degree. C., and a highly densified plasma CVD process is performed at about 100.degree. C. In these low temperature processes, it is difficult to obtain-a predetermined chucking property stably.
In the electrostatic chuck in which aluminum nitride is used for a material of the substrate member, we think it is effective to add a metal member having a low resistivity in the substrate member as shown in Japanese Patent Publication No. 7-19831. However, in the electrostatic chuck mentioned above, the metal member having a low resistivity and so on is detached from a surface of the substrate member, and thus there is a possibility of being a cause of semiconductor pollution. Therefore, it is not preferred to use the electrostatic chuck mentioned above for a highly purified semiconductor process such as a process for 8 inch wafer.